Definition of target in Linux kernel's Makefile

Question

I'm about to build linux kernel. Before moving to the build step, I have to configure the linux kernel with the command as below

make menuconfig

I can not find any definition of menuconfig in ./Makefile. I also grep-ed in the repo to look for the definition of the target and found nothing. So how does make runs some targets relating to Configuring the kernel like menuconfig, oldconfig, etc.

Answer 1

The kernel build system makes heavy use of GNU Make features. In the top-level Makefile, the rule for the menuconfig target is this one:

%config: outputmakefile scripts_basic FORCE
    $(Q)$(MAKE) $(build)=scripts/kconfig $@

That runs a sub-make for the target in "scripts/kconfig/Makefile". In "scripts/kconfig/Makefile", the rule for the menuconfig target is slightly obscured:

define config_rule
PHONY += $(1)
$(1): $(obj)/$($(1)-prog)
    $(Q)$$< $(silent) $(Kconfig)

PHONY += build_$(1)
build_$(1): $(obj)/$($(1)-prog)
endef

$(foreach c, config menuconfig nconfig gconfig xconfig, $(eval $(call config_rule,$(c))))